如何在同一字段的两个用户 ID 中获取第二个用户 ID

Question

I have a only two user chat that puts both user id's in a field (to make it a new id). I need to get the second Id and show letter in a list. How can I get the second part of the id after the hyphen

{
  "chat" : {
    "st98ySAm5CNeq2WVDTCAQJ3ZcpP2-2C95b9MJprgpCITMXknPuXS52mR2" : {
      "-M9Qk0mmv-r2C0kaFqpn" : {
        "_id" : 1591750954541,
        "createdAt" : 1591750954541,
        "order" : -1591750954541,
        "text" : "Hello there",
        "uid" : "2C95b9MJprgpCITMXknPuXS52mR2"
      },
      "-M9QkBv-rl18Nc4OyfpV" : {
        "_id" : 1591751000122,
        "createdAt" : 1591751000122,
        "order" : -1591751000122,
        "text" : "Hello",
        "uid" : "st98ySAm5CNeq2WVDTCAQJ3ZcpP2"
      }
    },
    "st98ySAm5CNeq2WVDTCAQJ3ZcpP2-heGJLHnvwMgofczT9PHSlRwANCB2" : {
      "-M9_eYajRuO0RjGDJHSM" : {
        "_id" : 1591917295564,
        "createdAt" : 1591917295564,
        "order" : -1591917295564,
        "text" : "Mmmm",
        "uid" : "heGJLHnvwMgofczT9PHSlRwANCB2"
      },
      "-M9_efDQ1qHUrLMndU2o" : {
        "_id" : 1591917327330,
        "createdAt" : 1591917327330,
        "order" : -1591917327330,
        "text" : "How are you BIG MAN",
        "uid" : "st98ySAm5CNeq2WVDTCAQJ3ZcpP2"
      }
    },
    "yKaXQZCbn8RdxO96tsbf9ZQHK3g1-2C95b9MJprgpCITMXknPuXS52mR2" : {
      "-M9QUli8eRb7gEEwgIM8" : {
        "_id" : 1591746694381,
        "createdAt" : 1591746694381,
        "order" : -1591746694381,
        "text" : "Hello",
        "uid" : "2C95b9MJprgpCITMXknPuXS52mR2"
      },
      "-M9Qji3QtqOKYrRZV7Wg" : {
        "_id" : 1591750873750,
        "createdAt" : 1591750873750,
        "order" : -1591750873750,
        "text" : "Hi bro",
        "uid" : "yKaXQZCbn8RdxO96tsbf9ZQHK3g1"
      },
      "-M9QjwXH4diBq0mj_aPz" : {
        "_id" : 1591750933005,
        "createdAt" : 1591750933005,
        "order" : -1591750933005,
        "text" : "Hi how are you",
        "uid" : "2C95b9MJprgpCITMXknPuXS52mR2"
      }
    }
  }
}

I split the id into to and took the second part but this way it makes multiple arrays each time it loops and and creates some empty objects

componentDidMount() {
    firebase
      .database()
      .ref()
      .child("chat")
      .on("child_added", snapshot => {
          const anotherUsers = [];
          let array = snapshot.key.split("-");
          let a = array[1];
          anotherUsers.push({
            key: a
          });
          this.setState({
            unknownUser2: anotherUsers
          });
     
      });
}

Answer 1

Try something like this

componentDidMount() {
    firebase
      .database()
      .ref()
      .child("chat")
      .on("child_added", snapshot => {
          const unknown = [...this.state.unknownUser2];
          let array = snapshot.key.split("-");
          let a = array[1];
          const updated=[...unKnown,{key: a}]
          this.setState({
            unknownUser2: updated
          });
     
      });
}

Answer 2

To show the second part of each key under chat , it is probably easier to use a value event:

firebase
  .database()
  .ref()
  .child("chat")
  .on("value", snapshot => {
      const anotherUsers = [];
      snapshot.forEach((child) => {
         const second = child.key.split("-")[1];
         anotherUsers.push({ key: second });
      });
      this.setState({
        unknownUser2: anotherUsers
      });
  });